Question

嘿，我正在使用MVC2中的帮助台，我遇到的问题是数据没有通过我的ViewModel从我的视图中传输。

在主页上，我有三个DropDownLists，您可以从中选择问题区域。然后，您可以按一个按钮报告问题或转到常见问题解答。如果您在DropDownLists中选择了一个问题区域，则该站点应记住您通过视图模型进行数据传输时所选择的内容。

但是当我进入Home索引的Post方法时，我的SelectLists和SelectListItems为空，而包含按钮信息的字符串包含正确的数据。

我做错了什么？

这是我的家庭控制器：

public ActionResult Index()
    {
        var viewModel = new HomeIndexViewModel()
        {
            // The lists with problem areas are populated.
            problemAreas1 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName"),
            problemAreas2 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName"),
            problemAreas3 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName")
        };
        return View(viewModel);
    }

    //
    // POST: /Home/

    [HttpPost]
    public ActionResult Index(HomeIndexViewModel viewModel)
    {
        // snip
    }

我的观点模型：

public class HomeIndexViewModel
{
    // A SelectList containing elements for the DropDownLists in the Home "Index" view.
    public SelectList problemAreas1 { get; set; }
    public SelectList problemAreas2 { get; set; }
    public SelectList problemAreas3 { get; set; }

    // Items chosen in the DropDownLists.
    public SelectListItem itemOne { get; set; }
    public SelectListItem itemTwo { get; set; }
    public SelectListItem itemThree { get; set; }

    // String for IDing what button is pressed.
    public string submitButton { get; set; }
}

我的家庭索引视图（继承自HomeIndexViewModel，我只是没有包含代码，因为它搞砸了帖子）：

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
<% using (Html.BeginForm("Index", "Home", FormMethod.Post))
   {%>
<h2>
    Search for your problem:</h2>
<asp:Label ID="Label1" runat="server" Width="300px">
Choose a problem area, and search for an answer to your problem in the FAQ, 
    or you can press the report button to report your problem.</asp:Label>
<%-- Here are the DropDownLists. --%>
<p style="width: 220px; height: 24px;">
    <%: Html.DropDownListFor(model => Model.itemOne, Model.problemAreas1, "Choose a problem area")%>
</p>
<p style="width: 220px;">
    <%: Html.DropDownListFor(model => Model.itemTwo, Model.problemAreas2, "Choose a problem area")%>
</p>
<p style="width: 220px">
    <%: Html.DropDownListFor(model => Model.itemThree, Model.problemAreas3, "Choose a problem area")%>
</p>
<p>
    <%-- Here are the two buttons allowing people to do a search or create a new ticket respectively. --%>
    <input type="submit" value="Search for problems" name="submitButton" id="searchButton" />
    <input type="submit" value="Report problem" name="submitButton" id="submitButton" />
</p>
<%} %>

感谢您的时间。： - ）

Answer 1

当您将表单提交回POST操作时，problemAreas1,2,3属性将为null是完全正常的，因为它们的内容从未发布。您需要以与GET操作相同的方式重新填充它们。就itemOne，Two，Three属性而言，它们应该是简单的字符串值而不是SelectListItem类型。

型号：

public class HomeIndexViewModel
{
    // A SelectList containing elements for the DropDownLists in the Home "Index" view.
    public SelectList problemAreas1 { get; set; }
    public SelectList problemAreas2 { get; set; }
    public SelectList problemAreas3 { get; set; }

    // Items chosen in the DropDownLists.
    public string itemOne { get; set; }
    public string itemTwo { get; set; }
    public string itemThree { get; set; }

    // String for IDing what button is pressed.
    public string submitButton { get; set; }
}

控制器：

public ActionResult Index()
{
    var viewModel = new HomeIndexViewModel()
    {
        // The lists with problem areas are populated.
        problemAreas1 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName"),
        problemAreas2 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName"),
        problemAreas3 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName")
    };
    return View(viewModel);
}

//
// POST: /Home/

[HttpPost]
public ActionResult Index(HomeIndexViewModel viewModel)
{
    if (!ModelState.IsValid)
    {
        // the model wasn't valid =>
        // show the same form so that the user can fix validation errors
        viewModel.problemAreas1 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName");
        viewModel.problemAreas2 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName");
        viewModel.problemAreas3 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName");
        return View(viewModel);
    }
    // TODO: everything went fine => update your database and redirect
    return RedirectToAction("Index");
}

Answer 2

我没有看到您的视图中的页面指令，让它知道您的模型？

这样的事情应该是你观点的第一行：

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<HomeIndexViewModel>" %>

Answer 3

您的选择列表将为null，因为该数据不会在表单中传回，这应该没问题。但是，因为它们为null，所以集合中没有SelectListItem MVC可以返回，因此它也是null。

尝试将以下内容添加到HomeIndexViewModel的构造函数中，而不是添加到控制器中（只是为了查看会发生什么）

problemAreas1 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName"), 
problemAreas2 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName"), 
problemAreas3 = new SelectList(helpDeskRepository.GetProblemAreas(), "ProblemAreaID", "ProblemAreaName")

我相信在返回POST时会发生绑定器将创建您的HomeIndexViewModel并填充SelectLists，并且应该能够填充您的SelectListItem。

但有些东西似乎有点可疑。我的直觉告诉我，SelectListItem不应该为空。

为什么我的ViewModel中没有传输数据？

3 个答案: